Changes in the phospholipid composition could be a response to changes in intracellular pH. Protons YH25448 need to be expelled at a higher rate when the pH drops. The LS 25 strain which showed faster growth rates than the other strains [9], was the only strain to up-regulate the F0F1 ATP synthase (Table 1), which at the expense of ATP expels protons during low pH. Regulation mechanisms Little is known about the regulation of catabolic pathways in L. sakei. Starting from ribose uptake, the rbs operon may be both relieved from repression and ribose induced. Presumably, a dual regulation of this operon by two opposite mechanisms,

substrate induction by ribose and CCR by glucose may occur in L. sakei. The ccpA gene was not regulated, consistent with this gene commonly showing constitutive expression in lactobacilli [42, 60]. The local PX-478 manufacturer repressor RbsR is homologous with CcpA, both belonging to the same LacI/GalR family of transcriptional regulators. RbsR was proposed to bind a cre-like consensus sequence located close to a putative CcpA cre site, both preceding rbsU [28]. RbsR in the Gram-positive soil bacterium Corynebacterium glutamicum was shown to bind a cre-like sequence, and using find more microarrays, the transcription of no other genes but the rbs operon was affected positively in an rbsR deletion mutant. It was concluded that RbsR influences the expression of only the rbs operon [61].

Similarily, in the L. sakei sequence, no other candidate members of RbsR regulation could be found [28]. However,

experiments are needed to confirm RbsR binding in L. sakei. In Bacillus subtilis, RbsR represent a novel interaction partner of P-Ser-HPr in a similar fashion to CcpA [62]. The P-Ser-HPr interaction is possible also in L. sakei as the bacterium exhibits HPr-kinase/phosphatase activity. A putative cre site is present in the promoter of lsa0254 encoding the second ribokinase (Table 2), and this gene is preceeded by the opposite oriented Oxymatrine gene lsa0253 encoding a transcriptional regulator with a sugar binding domain which belongs to the GntR family. This family of transcriptional regulators, as well as the LacI family which RbsR and CcpA belong to, are among the families to which regulators involved in carbohydrate uptake or metabolism usually belong [63]. The GntR-type regulator could possibly be involved in regulating the expression of the second ribokinase, or of the inosine-uridine preferring nucleoside hydrolase encoding iunH1 gene which is located further upstream of lsa0254. C. glutamicum possesses an operon encoding a ribokinase, a uridine transporter, and a uridine-preferring nucleoside hydrolase which is co-controlled by a local repressor together with the RbsR repressor of the rbs operon [60, 61, 64]. It is possible that such co-control could exist also in L. sakei. Ribose as well as nucleosides are products of the degradation of organic materials such as DNA, RNA and ATP.